Generally, the frames of desks and chairs, supporting frames, receiving frames, kitchen cabinets are based on the environments locating the frames so that these furniture are made as an integral merchandize. However, recently, under new concepts, the frames are designed as assembled and foldable elements for selling and transportation. This is because the conventional structure has a large volume and thus they are not suitable for transportation. Furthermore, if parts of these frames are destroyed, these improved designs are helpful in updating. Furthermore, the foldable structure is suitable for stacking a plurality of basic units with a small volume.
However, the inventors have referred to many kinds of the conventional and newly designs, but the inventor discovers that these designs still have the defects of occupying large volumes, high cost, and large stacking volumes and the inventor discovers that these defects are improvable.